Emission measurements by mass balance: In addition to emission estimates by the MOPED method the emissions from the broiler housing building were determined by an

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2. RESULTS AND DISCUSSION

2.1. Plume measurements: In total, 61 plume measurements were made downwind from the chicken farm, on five separate days, between 10:00 and 13:00 GMT on each day. A plume measurement constitutes one full traverse of the plume, recording the rise in concentration above background directly downwind of the source and the lateral spread of the downwind concentrations due to dispersion. Three of the measurement days (12/01, 31/01, 01/02) took place during southerly winds, therefore downwind measurements were made along the road to the North of the housing unit. From 26/01-27/01, the wind direction was ESE, thus the mobile measurement system had to move to the western side of the map to find the plume. During these days, plume measurements were made along the western road which runs North-South (Figure 1).

The fetch distance between the source and the measurement locations was of the order of 200-260m when measuring along the northern road and 520-580m when measuring along the western road.

Figure 1. Plume measurements downwind of the poultry housing building, showing the rise in concentration above background (TJ) measured on each run (60 plume measurements over five separate

days). The amplitude of the plume reflects the magnitude of the concentration levels, while the orientation is a function of the wind direction.

2.2. Emission estimates: Each plume measurement could provide an emission rate for the building, however due to stochastic variability in atmospheric dispersion; the accuracy of any one interval is limited, even under ideal circumstances (Flesch et al., 2004). Therefore we take the average of a number of individual estimates over a certain period, and compare against the reference mass-balance method. For the comparison between the two methods, the data was first filtered to include periods where both the MOPED and MB systems were in operation. Afterwards, a further filter was applied to

Measurement methods

remove periods where there was rainfall, as there was a strong indication that the plume concentration measurements were depleted in NH₃ due to wet deposition/washout, which we cannot account for using the dispersion model. The rainfall filter was very restrictive, removing all of the plume measurements made on 31/01 and a significant fraction of measurements on 27/01 and 01/02/ (50% of total plumes).

The average MB and MOPED emission estimates are given in Figure 2 and Table 1. There are three scenarios (heat balance, ventilation records, and SF6 tracer ventilation values) shown for the MB emissions and four shown for the MOPED emissions (deposition sensitivity scenarios). The bLS emission estimates are highly sensitive to deposition, where the fastest dry deposition parameterisation (Rc min 2) led to average values that are between 31 and 138% higher than the simulations without including deposition (nodep scenario). The fraction of NH3 deposited downwind of the source will depend upon the fetch distance between the source and receptor, which accounts for the greater sensitivity to deposition on the 26^th and 27^th January as plume measurements were made along the more distant western road (520-580m downwind). Additionally, the fraction of emitted NH3 that is deposited will be strongly influenced by the resistance of the canopy layer to deposition (p_^), as the presence of water films on the canopy surface is an efficient sink for NH3, while very dry conditions or fertilisation of the canopy surface can inhibit deposition (Spindler et al., 2001; Bell et al., 2017). The three deposition scenarios (Rc min 20, Rc min 10, and Rc min 2) provide an uncertainty range around this problem, as each describes the canopy resistance to deposition as a function of relative humidity (RH) (Equation 2, Spindler et al., 2001), however the parameter p^,qAB was set at 2, 10 and 20 to modify the strength of the humidity response across a realistic range.

p_^ = p_^,qAB rs(`tt u7/`i )v (3)

The MB emission estimates vary depending upon the selection of the ventilation rate used to calculate the emissions. The mass balance heat emission rates are systematically lower (22-27%) than the mass balance ventilation emission rates. This may be due to the heat balance model (CIGR, 2002), which may be underestimating the heat output of the broilers as the animals now grow more quickly due to advances in breeding (P. Robin, personal communication, 2017). However, it is also conceivable that the mechanical ventilation system can overestimate the ventilation rate of the building. The SF tracer

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with the MOPED method in this experiment is at least 20-30%. Had there been suitable downwind measurement locations nearer the source the sensitivity to p^ estimates would be lower. The MB and MOPED emission estimates on each measurement day agree within 20-30%, therefore the MOPED method appears to produce robust emission estimates relative to the MB reference. However, the standard deviation of the MB emission estimates are significantly higher than the MB emission estimates, indicating a low precision for the MOPED method in this particular example.

Figure 2. Average emissions estimated by MOPED and mass balance methods. The mass balance estimates show three scenarios depending on the emission rate applied (heat balance model, ventilation records or SF6 tracer). The MOPED emission estimates (bLS) indicate four scenarios for deposition: nodep – assuming no deposition; dep Rc min 2-20: with deposition and a minimum canopy resistance of 2, 10,

and 20 s m^-1 to explore the sensitivity of emission estimates to dry deposition. Error bars indicate the standard deviation of the emission estimates.

Table 1. Average NH3 emissions (Q, g NH3 s^-1) from the housing unit determined by the MOPED and MB methods. Different scenarios investigate the sensitivity to MB ventilation rate and MOPED dry deposition

selections. The standard deviation (SD) of the emission estimates are also given.

Date 26/01/2017 27/01/2017 01/02/2017

Emission estimate Q (g s^-1) SD (g s^-1) Q (g s^-1) SD (g s^-1) Q (g s^-1) SD (g s^-1)

MOPED nodep 0.1 0.04 0.06 0.03 0.13 0.05

dep Rc min 20 0.14 0.05 0.1 0.06 0.15 0.06

dep Rc min 10 0.15 0.05 0.12 0.07 0.16 0.07

dep Rc min 2 0.17 0.06 0.13 0.08 0.17 0.07

MB SF₆ 0.14 0.03 - - - -

Ventilation 0.15 0.01 0.18 0.01 0.22 0.02

Heat balance 0.12 0.01 0.13 0.01 0.16 0.02

Measurement methods

3. CONCLUSION: The MOPED method offers very significant practical advantages for determining emissions from farm-scale sources. Most importantly of which, no intrusive measurements are required inside of the building, while the mobile platform provides considerable freedom to choose downwind measurement locations based upon the prevailing wind direction. However, an individual plume measurement provides a

“snapshot” of the emissions, while we recommend that repeat traverses of the plume are made to provide an average emission rate. Although plume-to-plume variability was high, the averaged emission rate for the MOPED method agreed with the MB emission estimate for the same period to within 20-30%, indicating that this new method is promising. The most important uncertainty with the MOPED method in this example was NH3 dry deposition, where a large fraction (between 16-56%) was dry deposited before reaching the downwind concentration receptor. In addition, there was evidence that rainfall led to significant washout and wet deposition which depleted downwind concentrations, therefore the emission estimates presented here contain only periods where there was no rainfall.

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Bell, M., Flechard, C., Fauvel, Y., Häni, C., Sintermann, J., Jocher, M., Menzi, H., Hensen, A., Neftel, A., 2017. Ammonia emissions from a grazed field estimated by miniDOAS measurements and inverse dispersion modelling. Atmos. Meas. Tech., 10, 1875-1892.

CIGR, 2002. Climatization of animal houses—heat and moisture production at animal and house level. In: Pedersen, S., Sällvik, K. (Eds.), 4Th Report of CIGR Working Group.

Horsens, Denmark. Research Centre Bygholm, Danish Institute of Agricultural Sciences, P.O Box 536, DK-8700 Horsens, Denmark.

Flesch, T.K., Verge, X.P.C., Desjardins, R.L., Worth, D., 2013. Methane emissions from a swine manure tank in western Canada. Can J Anim Sci 93.

Flesch, T.K., Wilson, J.D., Harper, L.A., Crenna, B.P., Sharpe, R.R., 2004. Deducing ground-to-air emissions from observed trace gas concentrations: A field trial. J Appl Meteorol 43, 487-502.

Häni, C., 2017. bLSmodelR – An atmospheric dispersion model in R, R package version 3.2, available at:.http://www.agrammon.ch/documents-todownload/blsmodelr/

Leen, J.B., Yu, X.Y., Gupta, M., Baer, D.S., Hubbe, J.M., Kluzek, C.D., Tomlinson, J.M., Hubbell, M.R., 2013. Fast In Situ Airborne Measurement of Ammonia Using a Mid-Infrared Off-Axis ICOS Spectrometer. Environ Sci Technol 47, 10446-10453.

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ASSESSING AMMONIA REDUCING TECHNIQUES IN BEEF CATTLE BY THE USE OF AN